1. Field of the Invention
This invention relates to a speech recognition system which effects a scoring operation to select a word candidate or candidates by use of transition networks.
2. Description of the Related Art
Recently, various studies have been made on speech recognition systems and the speech recognition performance has been remarkably enhanced. In one of the speech recognition systems, input speech is acoustically analyzed to derive feature parameters thereof, the feature parameters are compared with or verified with reference to a dictionary prepared for each phonetic segment, such as a phoneme, to detect a segment lattice including a plurality of phoneme candidates and the similarity of the thus detected segment lattice, and then a word is recognized based on the detected segment lattice. As disclosed in U.S. Pat. No. 4,888,823, now U.S. Pat. No. 4,888,823 for example, with the above speech recognition system, the detected phonetic segment lattice is passed through previously constructed transition networks for respective words so as to derive several candidate words. In the process of deriving the candidate words, the scoring operation is effected in the transition network so as to output one of the candidate words which has the largest score as the result of recognition process.
However, such a simple scoring calculation may cause an erroneous word to be selected from a plurality of words which are similar to one another, resulting in an erroneous word recognition. That is, in a case where a plurality of words which are similar to one another are given as the candidate words, the result of scoring will be largely dependent on the scores given when the respective candidate words are passed through the transition networks.
Various conventional methods have been proposed as a method for determining the score. However, there is no method by which the proper scores can be derived for all of the starting and ending portions of each word and the transient portion of the speech, and therefore the occurrence of erroneous recognition can not be prevented.